JPH07302913A - Method for manufacturing semiconductor device - Google Patents

Abstract

(57) [Abstract] [Purpose] To form high quality polycrystalline semiconductor thin film by low temperature process. A semiconductor device including a thin film transistor having a semiconductor thin film 2 formed on an insulating substrate 1 as an active layer is manufactured. First, an amorphous semiconductor thin film 2 or a polycrystalline semiconductor thin film 2 having a relatively small grain size is formed on an insulating substrate 1. Next, the semiconductor thin film 2 is annealed by heat so that relatively large crystal grains are solid-phase grown. Then, the semiconductor thin film 2 is irradiated with a laser beam to remove the crystals remaining in the crystal grains and crystallize the amorphous portions remaining between the crystal grains.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device used as a drive substrate of an active matrix type liquid crystal display panel. More specifically, the present invention relates to a method for forming a polycrystalline semiconductor thin film used as an active layer.

[0002]

2. Description of the Related Art Development of an active matrix type liquid crystal display panel using a thin film transistor having a hydrogenated amorphous silicon thin film as an active layer has progressed, and it has become possible to realize an image quality equal to or higher than that of a CRT. Is building its position. A hydrogenated amorphous silicon thin film transistor can be formed at a process temperature of 350 ° C. or lower, for example, and a low-cost glass substrate can be used. However, there are many problems that must be solved in order to realize a manufacturing cost equivalent to that of a CRT. For example, the problem of the peripheral driver circuit using the IC chip and its mounting cost cannot be ignored.

The problem is large even in a liquid crystal display panel compatible with HDTV or a large-screen high-definition liquid crystal display panel. In these cases, it is necessary to increase the number of lines and increase the storage capacity of the pixel, and it is difficult to secure the aperture ratio of the pixel by reducing the device size in a hydrogenated amorphous silicon thin film transistor having low mobility. Furthermore, plasma CV
The amorphous silicon thin film formed by D has many traps, which makes the operation of the transistor unstable.

Considering the limit of such a hydrogenated amorphous silicon thin film transistor, the need for a process technology for forming a thin film transistor using a low temperature polycrystal silicon thin film as an active layer, which can be formed by a manufacturing process substantially equivalent to this, is increased. ing. Development of an active matrix type liquid crystal display panel in which peripheral driver circuits are integrated on a glass substrate using this is awaited.

In hydrogenated amorphous silicon thin film transistors, there are many metastable defects in the channel layer. This contributes to the change over time in the threshold voltage. On the contrary,
Polycrystalline silicon does not contain hydrogen and has a small number of metastable defects. Therefore, the polycrystalline silicon thin film transistor can be expected to operate stably. Instead, polycrystalline silicon has many dangling bonds at grain boundaries. These defects are located at the center of the band gap and serve as carrier generation / recombination centers. Therefore, the polycrystalline silicon thin film transistor generates a large leak current especially in the high electric field region near the drain. The advantage of polycrystalline silicon is that it has a high carrier mobility. It is more than two orders of magnitude larger than hydrogenated amorphous silicon. The carrier mobility of polycrystalline silicon is dominated by the potential barrier at grain boundaries. The field effect mobility varies exponentially with the size of this barrier. The development of high-mobility polycrystalline silicon has been studied with a focus on reducing the total number of defect densities by making crystal grains as large as possible. It is also important to reduce the defect density at the crystal grain boundaries to lower the height of the barrier.

[0006]

The solid phase growth method has been conventionally known as a technique for producing high quality polycrystalline silicon on a glass substrate by a low temperature process of 650 ° C. or lower. This is a method in which a silicon film is formed as a precursor film by the LPCVD method and this is thermally annealed. Looking at the relationship between the film formation conditions of the LPCVD method and the subsequent annealing conditions and the crystal grain size, amorphous silicon is formed at a low temperature of, for example, 580 ° C. or lower in order to obtain polycrystalline silicon having a large grain size. It has been found that it is preferable to anneal this at a low temperature of about 600 ° C. In the case of thermal annealing solid phase growth, it is necessary to heat the amorphous silicon film at 600 ° C. for a long time, but a film having a large crystal grain size and a large mobility has been realized. However, in the solid phase growth of thermal annealing, the crystal type is not constant, and when looking at the crystal image, many twin defects are found in the crystal grains. Furthermore, the non-crystal part remains between the crystal grains. Due to these defects, there is a problem in that the thin film transistor is deteriorated.

A laser annealing method has been conventionally used as a technique for forming high-quality polycrystalline silicon at a low temperature, and is disclosed in, for example, Japanese Patent Laid-Open No. 60-245124. In this method, the silicon thin film can be crystallized at a relatively low temperature without raising the temperature of the entire substrate. When a silicon thin film to be crystallized is irradiated with a laser pulse having a short wavelength, the laser light is absorbed only at the very surface of the silicon thin film, and then the inside of the thin film is melted and recrystallized by heat conduction. Alternatively, it is annealed to increase the crystal grains. The polycrystalline silicon thin film formed by this method has granular crystal grains substantially uniformly distributed. The lattice image is characterized in that the number of twin defects is much smaller than in the case of solid phase growth, and the lattice image is not disturbed at the grain boundaries. However, in the case of laser annealing, there is a problem that the size of crystal grains is relatively small, for example, 60 to 100 nm, and there are many crystal grain boundaries, which leads to deterioration in characteristics of thin film transistors.

[0008]

SUMMARY OF THE INVENTION In view of the above problems of the prior art, it is an object of the present invention to produce a high quality semiconductor thin film by a low temperature process. The following measures have been taken in order to achieve this object. That is, in a method of manufacturing a semiconductor device including a thin film element having a semiconductor thin film formed on an insulating substrate as an active layer, an amorphous semiconductor thin film or a polycrystalline semiconductor thin film having a relatively small grain size is formed on the insulating substrate. A step of forming a film, a step of annealing the semiconductor thin film to perform solid phase growth of crystal grains having a relatively large grain size, and irradiating the semiconductor thin film with laser light to remove defects remaining in the crystal grains and / or Or a step of crystallizing an amorphous portion remaining between crystal grains.

Further, in a semiconductor device including a thin film element having a polycrystalline semiconductor thin film formed on an insulating substrate as an active layer, the active layer contains crystal grains grown by solid phase by annealing and is irradiated with laser light. Is characterized in that defects are removed from the crystal grains, and at the same time, crystallization of the non-crystalline portion interposed between the crystal grains is achieved.

Further, it has a flat panel structure including an insulating substrate and a counter substrate which face each other with a predetermined gap therebetween, and a liquid crystal layer held in the gap, and the insulating substrate is provided with a polycrystalline semiconductor thin film as an active layer. In a liquid crystal display device in which a thin film transistor and a pixel electrode are formed in an integrated manner, and the counter electrode is formed on the counter substrate, the active layer contains crystal grains grown by solid phase by annealing, and a laser It is characterized in that the defects are removed from the crystal grains by light irradiation and that the non-crystalline portions existing between the crystal grains are crystallized.

[0011]

According to the present invention, a high quality polycrystalline semiconductor thin film is formed by a low temperature process of 650 ° C. or lower by using both thermal annealing and laser annealing. First, an amorphous or semiconductor thin film having a relatively small grain size is thermally annealed to cause solid-phase growth of a relatively large grain size.
Next, laser annealing is performed to remove the defects remaining in the crystal grains and crystallize the non-crystalline portions remaining between the crystal grains. As a result, the crystal grains contained in the active layer of a thin film transistor such as a thin film transistor become large and become close to a single crystal, and an amorphous region between crystal grains is crystallized or recrystallized, so that a current easily flows, and It contributes to the increase of on-current. Further, since the carrier trap density contained in the active layer of the thin film transistor becomes low, it becomes possible to reduce the leak current.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. 1A to 1C are process diagrams showing a semiconductor device manufacturing method according to the present invention. First, in the step (A), 40 to 15 semiconductor thin films 2 to be active layers of thin film transistors such as thin film transistors are formed on a transparent insulating substrate 1 made of low melting point glass or the like.
The film is formed with a thickness of 0 nm. In this example, 5 by the LPCVD method.
Amorphous silicon was deposited to a thickness of 60 nm at a temperature of 00 ° C. Next, thermal annealing was carried out at a temperature of 600 ° C. in a nitrogen atmosphere for 10 hours to cause solid-phase growth of relatively large crystal grains. Next, in step (B), the photoresist 3 was patterned on the surface of the semiconductor thin film 2. This photoresist 3
Using the as a mask, impurities are ion-implanted into the semiconductor thin film 2 to form a source region S and a drain region D. Arsenic was ion-implanted into the N-channel transistor, and boron was ion-implanted into the P-channel transistor. The impurity dose amount is set to, for example, 5 × 10 ¹⁵ / cm ² . Next, in step (C), after the used photoresist 3 is removed, an antireflection film 4 is formed on the semiconductor thin film 2. This is used for preventing reflection of laser light irradiation performed in a later step and is made of, for example, SiO ₂ or Si ₃ N ₄ . The antireflection film 4 is formed to a thickness of 20 to 100 nm according to the wavelength of the laser light used. In this embodiment, since a XeCl excimer laser is used as a laser light source, SiO ₂ is added to 6
An antireflection film 4 was formed with a thickness of 0 nm. Next, in the step (D), a laser pulse of 2 is applied from above the antireflection film 4.
Irradiation is performed with an energy density of 00 mJ / cm ^{2 to} 700 mJ / cm ² . At this time, the irradiation region of the laser beam includes at least an area section corresponding to one chip of the semiconductor device, and the laser pulse is irradiated by one shot. This laser annealing removes defects remaining in the crystal grains of the semiconductor thin film 2 and / or
Alternatively, crystallization of the non-crystalline portion remaining between crystal grains is promoted.

In step (E), the used antireflection film 4 is peeled off after the laser irradiation. Next, in step (F),
The crystallized silicon semiconductor thin film 2 is patterned into a predetermined shape to form an element region 5. Next, in step (G), the gate insulating film 6 is formed so as to cover the element region 5. In this example, the gate insulating film 6 was formed by depositing SiO ₂ with a thickness of 120 nm by the atmospheric pressure CVD method. Next, in the step (H), the gate electrode 7 is formed between the source region S and the drain region D formed previously.
Was formed. In this example, a metal film is formed on the gate insulating film 6 and then patterned into a predetermined shape to form a metal gate electrode 7. Subsequently, in step (I), SiO ₂ was deposited to a thickness of 300 nm to form the first passivation film 8. Next, in step (J), a contact hole was opened in the first passivation film 8 and a wiring 9 communicating with the source region S was formed.
Further, in the step (K), SiO ₂ was deposited to a thickness of 300 nm to form the second passivation film 10. Finally step (L)
Then, a contact hole is opened through the second passivation film 10 and the first passivation film 8 to expose the drain region D. After that, a transparent conductive film such as ITO is formed and then patterned into a predetermined shape to form the pixel electrode 11.

As described above, a semiconductor device including a thin film transistor having the polycrystalline semiconductor thin film 2 formed on the insulating substrate 1 as an active layer is completed. The active layer of the thin film transistor, that is, the element region 5 contains crystal grains that have been solid-phase grown by thermal annealing, and the defects have been removed from the crystal grains by laser annealing, and the crystal of the non-crystalline portion interposed between the crystal grains. Is being promoted.

A specific method of laser annealing will be described in detail with reference to FIG. As described above, in the semiconductor device manufacturing method according to the present invention, the semiconductor thin film 22 is first formed on the insulating substrate 21. Next, a series of treatments including a heat treatment of the semiconductor thin film 22 is performed to integrally form thin film transistors in the area section 23 for one chip. Finally, pixel electrodes for one screen are formed in the area section 23. As a result, a semiconductor device to be the display semiconductor chip 27 is manufactured. In this step, in the laser annealing, the area section 23 is irradiated with the laser pulse 28 in one shot to collectively crystallize the semiconductor thin film 22 for one chip. As shown, the cross-sectional shape of the laser pulse 28 matches the shape of the area section 23. Further, in the area section 23, finally, the matrix array 24, the horizontal scanning circuit 25, and the vertical scanning circuit 26 are integrally formed. Matrix array 2
Reference numeral 4 includes a thin film transistor and a pixel electrode, while the horizontal scanning circuit 25 and the vertical scanning circuit 26 in the peripheral driver section are composed of thin film transistors.

FIG. 3 shows a laser irradiation method which is performed when a large number of display semiconductor chips are formed from a large-sized transparent insulating substrate 51. As shown in the figure, a semiconductor thin film 52 is entirely formed on the transparent insulating substrate 51. Further, an antireflection film 53 is formed thereon. The laser annealing described above is performed by irradiating the laser pulse 54 through the antireflection film 53. At this time, a plurality of area sections 55 preset on the transparent insulating substrate 51 are successively irradiated with a laser pulse 54 for one shot. This can significantly improve the throughput of the film forming process.

FIG. 4 is a schematic perspective view showing an example of an active matrix type liquid crystal display device assembled by using the display semiconductor chip shown in FIG. As shown in the figure, the liquid crystal display device has a flat panel structure including an insulating substrate 101 and a counter substrate 102 which are arranged to face each other with a predetermined gap, and a liquid crystal layer 103 held in the gap. On the lower transparent insulating substrate 101, there are a thin film transistor 104 having a polycrystalline semiconductor thin film as an active layer and a pixel electrode 105.
And are formed in an integrated manner to form a matrix array 106. Further, a horizontal scanning circuit 107 and a vertical scanning circuit 108 which are also made of thin film transistors are formed in the peripheral portion of the insulating substrate 101. On the other hand, the counter substrate 1 on the upper side
A counter electrode (not shown) is formed on the inner surface of 02. In such a structure, the active layer serving as the element region of the thin film transistor 104 includes crystal grains that have been solid-phase grown by thermal annealing, and defects are removed from the crystal grains by laser annealing, and the amorphous layer interposed between the crystal grains. The part is crystallized.

Finally, the effects of the present invention will be described with reference to the graphs of FIGS. Each of these graphs shows the gate voltage Vgs / drain current Ids characteristics of the thin film transistor. The drain current Ids is represented by a logarithmic memory. FIG. 5 shows a case where a silicon polycrystalline semiconductor thin film formed only by conventional solid phase growth is used as an active layer, and FIG. 6 shows a silicon polycrystalline semiconductor thin film formed only by conventional laser annealing as an active layer. FIG. 7 shows a case where a silicon polycrystalline semiconductor thin film formed by combining solid phase growth and laser annealing according to the present invention is used as an active layer. With only solid-phase growth, crystal defects are contained in the crystal and non-crystalline portions remain between crystal grains. Therefore, as shown in the graph of FIG. 5, the characteristics of the thin film transistor are not always satisfactory. On the other hand, when crystallized by laser annealing, the crystal grains are generally small and there are many boundaries between the crystal grains. Therefore, as shown in the graph of FIG. 6, the electrical characteristics of the thin film transistor are not always satisfactory. On the other hand, when the solid phase growth and the laser annealing are combined, the crystal grains of the thin film transistor active layer become large and become close to a single crystal, and the amorphous region between the crystal grains is crystallized or recrystallized, so that the current is increased. It becomes easy to flow. Therefore, as shown in the graph of FIG. 7, the on-current of the thin film transistor is increased as compared with the cases of FIGS. Further, the carrier trap density of the thin film transistor active layer becomes low. Therefore, the leakage current is reduced as shown in the graph of FIG.

[0019]

As described above, according to the present invention, the semiconductor thin film is first annealed to grow the crystal grains having a relatively large grain size in the solid phase. Next, laser annealing is performed to remove crystals remaining in the crystal grains and / or to crystallize non-crystalline portions remaining between the crystal grains. As a result, the crystal grains of the thin film transistor active layer become larger and become closer to a single crystal, and the amorphous region between the crystal grains is crystallized or recrystallized so that a current easily flows, which contributes to an increase in the on-current of the thin film transistor. effective. Further, there is an effect that the carrier trap density of the thin film transistor active layer becomes low and the leak current can be reduced.

[Brief description of drawings]

FIG. 1 is a process chart showing a semiconductor device manufacturing method according to the present invention.

FIG. 2 is a schematic diagram showing an example of a laser annealing process.

FIG. 3 is a schematic diagram showing a laser annealing process similarly.

FIG. 4 is a schematic perspective view showing an example of a liquid crystal display device assembled by using the semiconductor device manufactured according to the present invention.

FIG. 5 is a graph showing electric characteristics of a thin film transistor having a polycrystalline semiconductor thin film formed by thermal annealing as an active layer.

FIG. 6 is a graph showing electric characteristics of a thin film transistor having a polycrystalline semiconductor thin film formed by laser annealing as an active layer.

FIG. 7 is a graph showing the electrical characteristics of a thin film transistor having an active layer of a polycrystalline semiconductor thin film formed by solid phase growth and laser irradiation.

[Explanation of symbols]

 1 Insulating Substrate 2 Semiconductor Thin Film 4 Antireflection Film 5 Element Area 6 Gate Insulating Film 7 Gate Electrode 11 Pixel Electrode

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location H01L 21/20 27/12 R (72) Inventor Shizuo Nishihara 6-7 Kita-Shinagawa, Shinagawa-ku, Tokyo No. 35 Inside Sony Corporation (72) Inventor Hisao Hayashi 6-7 35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation

Claims (3)

[Claims] 1. A method of manufacturing a semiconductor device including a thin film element having a semiconductor thin film formed on an insulating substrate as an active layer, comprising: an insulating semiconductor thin film or a polycrystalline thin film having a relatively small grain size. A step of forming a semiconductor thin film; a step of annealing the semiconductor thin film to perform solid phase growth of relatively large-sized crystal grains; and a step of irradiating the semiconductor thin film with laser light to detect defects remaining in the crystal grains. A step of removing and / or crystallizing an amorphous portion remaining between crystal grains. 2. A semiconductor device including a thin film element having a polycrystalline semiconductor thin film formed on an insulating substrate as an active layer, wherein the active layer contains crystal grains grown by solid phase by annealing, and is irradiated by laser light. A semiconductor device characterized in that defects are removed from the crystal grains and that an amorphous portion interposed between the crystal grains is crystallized. 3. A flat panel structure including an insulating substrate and a counter substrate facing each other with a predetermined gap and a liquid crystal layer held in the gap, wherein the insulating substrate is provided with a polycrystalline semiconductor thin film as an active layer. A thin film transistor and a pixel electrode to be integrated are formed, a liquid crystal display device in which a counter electrode is formed on the counter substrate, wherein the active layer includes crystal grains grown by solid phase by annealing, Further, a liquid crystal display device is characterized in that defects are removed from the crystal grains by laser light irradiation, and crystallization of non-crystalline portions interposed between the crystal grains is achieved.